The present invention concerns a balancing device for traction forces, specifically intended for a hoist, that is supposed to simultaneously wind or unwind two or more traction cables, as well as a hoist fitted with such a device and a gondola equipped with at least one hoist as hereinabove.
Such hoists, particularly those comprising a twin winding organ, traction drums or traction sheaves where each of said organs carries its own cable, find numerous applications. Particularly in certain configurations they are employed for lifts or more specifically for gondolas engaged in the cleaning and/or upkeep of the facades of high-rise buildings. Such a gondola usually is held by four cables, a first pair of cables being arranged at a first short side of the gondola and the second pair of cables being arranged at the second short side of the gondola. Each pair of cables is wound/unwound from a hoist equipped with two drums, with each hoist having its own motor that is controlled independently of the other motor. Thus, the speed of winding/unwinding of each hoist is so adjusted by known mechanical, electric, or electronic means that each pair of cables is unwound or wound with the same speed and the gondola will remain horizontal. For the two cables of a given pair, to the contrary, since their winding or unwinding speed is controlled by a single hoist or by just one motor, said means cannot be employed to preserve their balance. An unbalance between the two cables of a pair may arise, for instance, when the winding of one of the cables on its drum is irregular and causes subsequent windings to be wound with a larger diameter than that of the windings of the other cable. In this case the cable being wound up on a larger diameter will tend to assume the full traction force, which may lead to
an unbalance of the gondola or, by rupture of this overly loaded cable, to risk for the workers riding this gondola.
A first mechanical means that allows an identical tensile stress to be preserved for the two cables of a given pair, even in a situation where one of the cables is poorly wound, consists of bringing the two cables together on one sheave. Such a device may be dangerous in the instance of rupture of one of the cables, since the other cable then becomes free, and the gondola is no longer held by either of the two cables.
According to other means, the two cables are attached to the two ends of a spreader while the center of this spreader is hinged to the suspension beam or to the gondola. This device will not encounter the drawback mentioned earlier, but now the difference in lengths that can be admitted between the two cables is limited by the length of the spreader.
In the two means described above, the balancing devicexe2x80x94sheave spider or center of the spreaderxe2x80x94is attached to the gondola or suspension beam in a single point, which in the final analysis is detrimental to the gondola""s balance. FR-A-2 183 594 describes a device with differential for a crane lifting hoist. Using this device the operator controls sequentially rather than simultaneously a lifting operation and a mast telescoping operation. There is no indication anywhere in this document that the device permits a simultaneous actuation of both drums.
WO 88/05999 describes a differential device allowing the forces on two traction cables of a trawl to be balanced. This document explicitly describes that the operations of launching of the trawl as well as those of hauling it in do not involve the use of the differential device, which is put in operation, only during the fishing, that is, when the hoists are inactive.
The invention provides a force balancing device for a hoist intended for at least one pair of traction cables that will allow the drawbacks mentioned earlier to be avoided.
It is an objective of the invention to propose a hoist that is intended for at least one pair of traction cables and is fitted with at least one force balancing device that is capable of ensuring at all times the safety of the object suspended on the cables.
It is yet another objective of the invention to propose a gondola for facade upkeep that is fitted with at least one hoist equipped with a force balancing device.
These objectives are attained by a balancing device, a hoist, and a gondola having the characteristics mentioned in the independent claims, while specific embodiments or variants are described in the dependent claims.
The below description describes several embodiments of a device according to the invention, and should be read in conjunction with the attached drawing comprising the figures where